[CIR] Upstream support for function-level variable decompositions #151073

mmha · 2025-07-29T02:30:44Z

This implements support for structured bindings on a function scope level. It does not add support for global structured bindings.

llvmbot · 2025-07-29T02:31:16Z

@llvm/pr-subscribers-clangir

@llvm/pr-subscribers-clang

Author: Morris Hafner (mmha)

Changes

This implements support for structured bindings on a function scope level. It does not add support for global structured bindings.

Full diff: https://github.com/llvm/llvm-project/pull/151073.diff

5 Files Affected:

(modified) clang/include/clang/CIR/MissingFeatures.h (+1)
(modified) clang/lib/CIR/CodeGen/CIRGenDecl.cpp (+6-2)
(modified) clang/lib/CIR/CodeGen/CIRGenExpr.cpp (+5)
(modified) clang/lib/CIR/CodeGen/CIRGenModule.cpp (+6-1)
(added) clang/test/CIR/CodeGen/variable-decomposition.cpp (+55)

diff --git a/clang/include/clang/CIR/MissingFeatures.h b/clang/include/clang/CIR/MissingFeatures.h
index e1a5c3d9ca337..d6501961dbe95 100644
--- a/clang/include/clang/CIR/MissingFeatures.h
+++ b/clang/include/clang/CIR/MissingFeatures.h
@@ -215,6 +215,7 @@ struct MissingFeatures {
   static bool intrinsics() { return false; }
   static bool isMemcpyEquivalentSpecialMember() { return false; }
   static bool isTrivialCtorOrDtor() { return false; }
+  static bool lambdaCaptures() { return false; }
   static bool lambdaFieldToName() { return false; }
   static bool loopInfoStack() { return false; }
   static bool lowerAggregateLoadStore() { return false; }
diff --git a/clang/lib/CIR/CodeGen/CIRGenDecl.cpp b/clang/lib/CIR/CodeGen/CIRGenDecl.cpp
index a28ac3c16ce59..97cfec5475dfe 100644
--- a/clang/lib/CIR/CodeGen/CIRGenDecl.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenDecl.cpp
@@ -608,11 +608,16 @@ void CIRGenFunction::emitDecl(const Decl &d) {
   case Decl::UsingDirective: // using namespace X; [C++]
     assert(!cir::MissingFeatures::generateDebugInfo());
     return;
-  case Decl::Var: {
+  case Decl::Var:
+  case Decl::Decomposition: {
     const VarDecl &vd = cast<VarDecl>(d);
     assert(vd.isLocalVarDecl() &&
            "Should not see file-scope variables inside a function!");
     emitVarDecl(vd);
+    if (auto *dd = dyn_cast<DecompositionDecl>(&vd))
+      for (BindingDecl *b : dd->bindings())
+        if (VarDecl *hd = b->getHoldingVar())
+          emitVarDecl(*hd);
     return;
   }
   case Decl::OpenACCDeclare:
@@ -632,7 +637,6 @@ void CIRGenFunction::emitDecl(const Decl &d) {
   case Decl::ImplicitConceptSpecialization:
   case Decl::TopLevelStmt:
   case Decl::UsingPack:
-  case Decl::Decomposition: // This could be moved to join Decl::Var
   case Decl::OMPDeclareReduction:
   case Decl::OMPDeclareMapper:
     cgm.errorNYI(d.getSourceRange(),
diff --git a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
index 7ff5f26be21b4..a2a9e719861f2 100644
--- a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
@@ -584,6 +584,11 @@ LValue CIRGenFunction::emitDeclRefLValue(const DeclRefExpr *e) {
     return lv;
   }
 
+  if (const auto *bd = dyn_cast<BindingDecl>(nd)) {
+    assert(!e->refersToEnclosingVariableOrCapture() && !cir::MissingFeatures::lambdaCaptures());
+    return emitLValue(bd->getBinding());
+  }
+
   cgm.errorNYI(e->getSourceRange(), "emitDeclRefLValue: unhandled decl type");
   return LValue();
 }
diff --git a/clang/lib/CIR/CodeGen/CIRGenModule.cpp b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
index 350270518156e..2f750153f5ee3 100644
--- a/clang/lib/CIR/CodeGen/CIRGenModule.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenModule.cpp
@@ -1244,8 +1244,13 @@ void CIRGenModule::emitTopLevelDecl(Decl *decl) {
     break;
   }
 
-  case Decl::Var: {
+  case Decl::Var:
+  case Decl::Decomposition: {
     auto *vd = cast<VarDecl>(decl);
+    if(isa<DecompositionDecl>(decl)) {
+      errorNYI(decl->getSourceRange(), "global variable decompositions");
+      break;
+    }
     emitGlobal(vd);
     break;
   }
diff --git a/clang/test/CIR/CodeGen/variable-decomposition.cpp b/clang/test/CIR/CodeGen/variable-decomposition.cpp
new file mode 100644
index 0000000000000..b82e0c62424d4
--- /dev/null
+++ b/clang/test/CIR/CodeGen/variable-decomposition.cpp
@@ -0,0 +1,55 @@
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-pc-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-pc-linux-gnu -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --check-prefix=LLVM --input-file=%t-cir.ll %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-pc-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --check-prefix=OGCG --input-file=%t.ll %s
+
+struct some_struct {
+    int a;
+    float b;
+};
+
+float function() {
+    auto[a, b] = some_struct{1, 2.f};
+
+    return a + b;
+}
+
+// CIR-LABEL: cir.func dso_local @_Z8functionv() -> !cir.float
+// CIR:  %[[RETVAL:.+]] = cir.alloca !cir.float, !cir.ptr<!cir.float>, ["__retval"]
+// CIR:  %[[STRUCT:.+]] = cir.alloca !rec_some_struct, !cir.ptr<!rec_some_struct>, [""]
+// CIR:  %[[MEMBER_A:.+]] = cir.get_member %[[STRUCT]][0] {name = "a"} : !cir.ptr<!rec_some_struct> -> !cir.ptr<!s32i>
+// CIR:  %[[LOAD_A:.+]] = cir.load align(4) %[[MEMBER_A]] : !cir.ptr<!s32i>, !s32i
+// CIR:  %[[CAST_A:.+]] = cir.cast(int_to_float, %[[LOAD_A]] : !s32i), !cir.float
+// CIR:  %[[MEMBER_B:.+]] = cir.get_member %[[STRUCT]][1] {name = "b"} : !cir.ptr<!rec_some_struct> -> !cir.ptr<!cir.float>
+// CIR:  %[[LOAD_B:.+]] = cir.load align(4) %[[MEMBER_B]] : !cir.ptr<!cir.float>, !cir.float
+// CIR:  %[[ADD:.+]] = cir.binop(add, %[[CAST_A]], %[[LOAD_B]]) : !cir.float
+// CIR:  cir.store %[[ADD]], %[[RETVAL]] : !cir.float, !cir.ptr<!cir.float>
+// CIR:  %[[RET:.+]] = cir.load %[[RETVAL]] : !cir.ptr<!cir.float>, !cir.float
+// CIR:  cir.return %[[RET]] : !cir.float
+
+// LLVM-LABEL: define dso_local float @_Z8functionv()
+// LLVM:  %[[RETVAL:.+]] = alloca float, i64 1
+// LLVM:  %[[STRUCT:.+]] = alloca %struct.some_struct, i64 1
+// LLVM:  %[[GEP_A:.+]] = getelementptr %struct.some_struct, ptr %[[STRUCT]], i32 0, i32 0
+// LLVM:  %[[LOAD_A:.+]] = load i32, ptr %[[GEP_A]]
+// LLVM:  %[[CAST_A:.+]] = sitofp i32 %[[LOAD_A]] to float
+// LLVM:  %[[GEP_B:.+]] = getelementptr %struct.some_struct, ptr %[[STRUCT]], i32 0, i32 1
+// LLVM:  %[[LOAD_B:.+]] = load float, ptr %[[GEP_B]]
+// LLVM:  %[[ADD:.+]] = fadd float %[[CAST_A]], %[[LOAD_B]]
+// LLVM:  store float %[[ADD]], ptr %[[RETVAL]]
+// LLVM:  %[[RET:.+]] = load float, ptr %[[RETVAL]]
+// LLVM:  ret float %[[RET]]
+
+// OGCG: @__const._Z8functionv.{{.*}} = private unnamed_addr constant %struct.some_struct { i32 1, float 2.000000e+00 }
+// OGCG-LABEL: define dso_local noundef float @_Z8functionv()
+// OGCG:  %[[STRUCT:.+]] = alloca %struct.some_struct
+// OGCG:  call void @llvm.memcpy.p0.p0.i64(ptr align 4 %[[STRUCT]], ptr align 4 @__const._Z8functionv.{{.*}}, i64 8, i1 false)
+// OGCG:  %[[GEP_A:.+]] = getelementptr inbounds nuw %struct.some_struct, ptr %[[STRUCT]], i32 0, i32 0
+// OGCG:  %[[LOAD_A:.+]] = load i32, ptr %[[GEP_A]]
+// OGCG:  %[[CAST_A:.+]] = sitofp i32 %[[LOAD_A]] to float
+// OGCG:  %[[GEP_B:.+]] = getelementptr inbounds nuw %struct.some_struct, ptr %[[STRUCT]], i32 0, i32 1
+// OGCG:  %[[LOAD_B:.+]] = load float, ptr %[[GEP_B]]
+// OGCG:  %[[ADD:.+]] = fadd float %[[CAST_A]], %[[LOAD_B]]
+// OGCG:  ret float %[[ADD]]

github-actions · 2025-07-29T02:33:56Z

✅ With the latest revision this PR passed the C/C++ code formatter.

bcardosolopes · 2025-07-29T14:50:59Z

clang/test/CIR/CodeGen/variable-decomposition.cpp

+};
+
+float function() {
+    auto[a, b] = some_struct{1, 2.f};


nit on 2 spaces

xlauko · 2025-07-29T15:03:32Z

clang/lib/CIR/CodeGen/CIRGenDecl.cpp

+    if (auto *dd = dyn_cast<DecompositionDecl>(&vd))
+      for (BindingDecl *b : dd->bindings())
+        if (VarDecl *hd = b->getHoldingVar())
+          emitVarDecl(*hd);


This differs from classic codegen. Can we align here, i.e. introduce maybeEmitDeferredVarDeclInit and use the same implementation as CodeGenFunction::MaybeEmitDeferredVarDeclInit

andykaylor · 2025-07-29T16:38:28Z

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

+    assert(!e->refersToEnclosingVariableOrCapture() &&
+           !cir::MissingFeatures::lambdaCaptures());


Can you make this use errorNYI instead?

erichkeane

1 nit, else lgtm.

erichkeane · 2025-07-31T14:36:40Z

clang/lib/CIR/CodeGen/CIRGenDecl.cpp

+      if (auto *hd = b->getHoldingVar())
+        emitVarDecl(*hd);
+  }
+}


Need a newline at the end here.

It surprises me a little that clang-format didn't catch this.

This implements support for structured bindings on a function scope level. It does not add support for global structured bindings.

* reformat rest

mmha requested review from lanza, bcardosolopes, xlauko and andykaylor as code owners July 29, 2025 02:30

llvmbot added clang Clang issues not falling into any other category ClangIR Anything related to the ClangIR project labels Jul 29, 2025

bcardosolopes approved these changes Jul 29, 2025

View reviewed changes

xlauko reviewed Jul 29, 2025

View reviewed changes

andykaylor reviewed Jul 29, 2025

View reviewed changes

mmha mentioned this pull request Jul 30, 2025

[CIR] Support more declarations without any codegen #151076

Merged

mmha force-pushed the cxx-variable-decompositions branch from 805bbd8 to 2676b6a Compare July 30, 2025 15:56

erichkeane approved these changes Jul 31, 2025

View reviewed changes

mmha added 4 commits July 31, 2025 16:45

[CIR] Upstream support for function-level variable decompositions

ebedb14

This implements support for structured bindings on a function scope level. It does not add support for global structured bindings.

clang-format

681fdf5

* introduce maybeEmitDeferredVarDeclInit

36331c3

* reformat rest

Add missing newline

a161ab1

mmha force-pushed the cxx-variable-decompositions branch from 2676b6a to a161ab1 Compare July 31, 2025 14:45

mmha merged commit 8a5d363 into llvm:main Jul 31, 2025
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[CIR] Upstream support for function-level variable decompositions #151073

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		assert(!e->refersToEnclosingVariableOrCapture() &&
		!cir::MissingFeatures::lambdaCaptures());

[CIR] Upstream support for function-level variable decompositions #151073

[CIR] Upstream support for function-level variable decompositions #151073

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